Field of the Invention
The present application relates to a thin diamond film, substrate, or window that has at least one optically-finished surface. The diamond film, substrate, or window has a large aspect ratio, defined as a largest dimension over thickness. The present invention also relates to a process of producing the diamond film, substrate, or window.
Description of Related Art
Diamond is the hardest material known, having a Mohs Hardness of 10, which makes diamond useful for applications such as cutting, machining, drilling, milling, etc. Diamond is also the most thermally conductive material known, having a thermal conductivity up to 2000 to 2200 watts per meter per Kelvin, which makes it desirable for applications in thermal management under demanding conditions. Diamond also has a low coefficient of friction, which makes it a versatile material for uses such as brakes. With diamond on diamond, it is the low wear coefficient and lubricating uses under extreme conditions which makes it advantageous. Diamond is also an excellent optical material for transmitting microwave, infrared, visible, and other ultraviolet electromagnetic waves. Diamond is also highly stable when used as detector for high fluence nuclear radiation. In addition, diamond is also highly inert in a chemical environment that might involve strong acid, strong base, strong oxidizing agent, or strong reducing agent, even at elevated temperatures or at cryogenic conditions. Furthermore, diamond has a high refractive index, which leads to its popular use in jewelry.
Though diamond is a versatile and premium material, its availability is limited in nature. Diamond mined from the earth is typically single crystal whose geometrical dimensions are limited in size and, often, too small for industrial uses that require large dimensions. Many times, diamond formed in nature contains impurities and crystal defects. A diamond crystal that is relatively large in crystal size, relatively pure in chemical contents, and relatively perfect without crystal defects is very expensive—often times, priceless.
Synthetic diamond is known to be produced industrially in chemical reactors under extremely high pressures and extremely high temperatures (the HTHP process). Due to such harsh synthetic conditions, the reactor size is limited, as are as the dimensions of the diamond. This process is also associated with high costs in process, equipment, and safety, related to harsh and demanding diamond growth conditions. Often times, the HTHP process produces diamond that has a yellow tint due to the incorporation of catalytic impurities into diamond lattices. In addition, the HTHP process is not able to produce diamond wafers of large diameter.
Industrially, diamond can also be grown in reactors in a process called chemical vapor deposition (CVD), where suitable growth conditions can be achieved by microwave-enhanced plasma, tungsten hot-filament, DC-Jet plasma, laser-induced plasma, acetylene-torch, etc. It is well known in the art that the CVD growth processes can also successfully grow polycrystalline diamond thin films on different substrates and/or free standing diamond thick films, though it is challenging to obtain low stress films or non-cracking diamond of significant size.
In many diamond applications, the surface of a diamond film, substrate, or window needs to be optically smooth for the purpose of transmitting light or electromagnetic waves, working as sound wave medium, as a substrate to reflect light/electromagnetic waves, or conduct heat energy away from electronics, photonics, or optoelectronics via a bonding mechanism such as brazing or gluing.
Because diamond is one of the hardest materials in the world, polishing diamond can be slow, expensive, and can generate a great deal of heat. Therefore, holding diamond in place by adhesive during polishing is not a good option since frictionally-generated heat can melt or destroy the adhesive. Moreover, diamond is also fragile and easy to shatter. In addition, the CVD growth of a diamond film, substrate, or window is a slow process, requiring expensive capital equipment, that uses a lot of electric energy for the diamond to grow in a very small area. Therefore, CVD diamond is expensive and many applications only require a thin diamond substrate or window if the requirement for one or more optically-finished diamond surface(s) can be fulfilled.
When a diamond film, substrate, or window is very thin (e.g., ≤400 microns in thickness), holding the diamond film, substrate, or window in place during polishing is challenging, particularly when the diamond film, window, or substrate reaches a thickness ≤400 microns, which is particularly true when the diamond film, substrate, or window has at least one large dimension (25 mm or greater), e.g. diameter. Beyond the limitations in polishing a thin diamond film, window, or substrate to an optically-finished surface(s), there are also challenges in successful polishing and fabricating diamond parts with a high aspect ratio (the ratio of the greatest dimension, e.g., without limitation, diameter, to the thickness), particularly when the aspect ratio of the diamond part is 100 or greater.
There is a need to produce large area diamond films, windows, or substrates that are thin and with one or both sides of the diamond surfaces optically finished. There is also a need to produce diamond films, windows, or substrates, thin (less than 400 microns in thickness) or thick (400 microns or thicker), having aspect ratios of 100 or greater, particularly for diamond parts having a largest dimension (e.g., without limitation, diameter) of 30 mm or greater. For light or electromagnetic wave management, a piece of diamond having a non-planar surface such as a dome, a cone, a pyramid, or any non-planar geometry is also needed for taking advantage of diamond's unique properties.